Recently, in line with miniaturization, lightweight, thin profile, and portable trends in electronic devices according to the development of information and telecommunications industry, the need for high energy density batteries used as power sources of such electronic devices has increased. Currently, research into lithium secondary batteries, as batteries that may best satisfy the above need, has actively conducted.
Currently, a carbon material is being used as an anode active material for a lithium secondary battery, and in particular, graphite having high crystallinity has mainly been used. Graphite has a layered structure, and lithium ions are intercalated between graphite layers from edges of the graphite layers during charge to form a graphite intercalation compound.
However, since most graphite has a flake-like morphology, a layer surface is deposited parallel to the surface of a current collector during the formation of an anode. Accordingly, the edges of the graphite layers are disposed perpendicular to a cathode, and thus, the lithium ions deintercalated from the cathode during the charge may not be smoothly intercalated between the graphite layers.
In particular, since the diffusion of lithium ions into graphite may not be sufficiently performed during high current charge, discharge capacity may decrease.
Also, since the lithium secondary battery generally uses a constant current-constant voltage charge method for charging and a constant current discharge method for discharging, lithium ions intercalated into the deep in graphite crystals at a low current during constant voltage charge may remain in the graphite without being completely discharged during high-rate discharge. Thus, it may be a cause of leading to cycle deterioration of graphite.
In particular, in a typical lithium secondary battery, since the lithium ions deintercalated from the cathode during the charge may not be smoothly intercalated between the graphite layers as described above, more lithium ions may remain in the graphite and the deterioration of cycle characteristics may increase.